AC voltage regulators are used to closely control and regulate the AC voltage level being delivered to a load connected to the output of the AC voltage regulator, regardless of the AC voltage variation at the input of the AC voltage regulator.
This has been traditionally done by various low frequency (LF), typically at 50 or 60 Hz, or other frequencies, electrical mains magnetic structures. These structures are typically tapped at specific discrete transformer voltage taps in various transformers or transformer configurations. Nonetheless, all these structures rely on traditional AC switching devices such as relays or semiconductor devices such as silicon-controlled rectifiers (SCR)'s or gate turn off thyristor (GTO)'s connected as anti-parallel AC switches, TRIAC's, AC switches such as insulated-gate bipolar transistors (IGBT)'s, MOSFET transistors, and SCR's configured as AC switches, e.g. connected between rectifiers. These AC switches are selected and activated by the electronic control circuit to automatically switch the selected magnetic transformer structure tap, in turn adjusting the transformer or transformer configuration turns ratio to control the AC output voltage as close as possible to the desired level.
Another traditional method to regulate an output AC voltage is to use an electro-mechanically-adjusted auto-transformer that is driven by electrical mechanical means, such as a controlled electrical motor. The electronic control in this case senses the input voltage and then drives the electro-mechanical means to move the output contact to adjust the turns of the auto-transformer, in turn sets the correct turns ratio to fix the output AC voltage to the desired level. These electro-mechanically-adjusted auto-transformer devices are also LF magnetic structures, typically at 50 Hz or 60 Hz, or other frequencies, and generally use carbon brushes to make the moving electrical contact to the auto-transformer windings. These brushes, however, undergo mechanical wear as such they need frequent maintenance and replacement.
A more sophisticated fully electronic version utilizes again LF mains transformers, typically at 50 Hz or 60 Hz, or other frequencies, connected in series between the AC input and the AC output of the voltage regulator. As the input AC voltage level varies, the AC voltage regulator electronic control senses the input voltage level, and then sets up an in-phase positive or an in-phase negative differential AC voltage that adds or subtracts, to or from, the varying input AC voltage to maintain the output AC voltage to the desired set level. This traditional approach, in its various forms, still uses LF mains frequency transformers or LF magnetic structures, typically at 50 Hz or 60 Hz, or other frequencies. In one configuration, the power electronics generates a LF mains frequency to correct the input AC voltage by a high frequency pulse width modulation (HF PWM) means, and this in-phase correction voltage to adjust the input AC mains voltage, is applied to the primary of the LF transformer, with the secondary of the LF transformer connected in series between the input and output of the AC power line. But still the magnetic structures used in these configurations, even though the power electronics operate at higher PWM frequencies, the final differential AC waveform is still applied to the LF series transformer, typically at 50 Hz or 60 Hz, or other frequencies, hence the LF transformer or magnetic structures still have the disadvantage of size and weight.
The voltage regulator disclosed in U.S. patent application Ser. No. 14/525,230 (the disclosure of which is incorporated herein by reference in its entirety) also addresses the disadvantages of the traditional designs in using series low mains frequency, large, and heavy magnetic structures. Since the size of any magnetics is largely inversely proportional to its operating frequency, the present invention approaches with this as a central design parameter. The aim of the '230 voltage regulator is to achieve a unique AC voltage regulator topology that utilizes only HF (e.g. 1 KHz to 1000 kHz) series magnetic structures that reduce significantly the size, weight, and cost of these magnetic structures. The '230 voltage regulator, however, uses bidirectional AC switches that exhibit additional losses.